1. Field of the Invention
The present invention relates to methods and apparatus for tumbling concrete products and more particularly to such methods and apparatus in which concrete products are tumbled in a drum having an elastic liner.
2. Background of the Invention
It is known to provide a textured surface for concrete products, such as concrete blocks, by putting the blocks in a cylindrical drum having an elastic liner and rotating the drum. This chips the surface and provides a desirable textured appearance. The drum typically includes an input end that is elevated slightly relative to an output end. As a result, the blocks move toward the lower output end of the drum where they emerge, ready for shipping. While moving down the drum, the blocks tumble against one another, thus chipping the blocks.
The elastic liner is a suitable elastic material such as rubber. In one prior art tumbler, coaxial ribs, each including a cylindrical inner surface, are positioned adjacent one another along the length of the drum. A rubber strip is bolted to and covers each rib. The bolts are received through holes bored in the rubber and corresponding bores in the ribs. When the rubber is worn out, the bolts are removed, bores are drilled in new rubber strips, and the new rubber strips are bolted onto the ribs.
In another prior art drum, tire retread strips are placed on the radially inner drum surface parallel to the longitudinal axis. The strips are secured to the drum by bolts received in bores drilled through the strips and corresponding drum bores. As in the other prior art tumbler, when the tire retread strips are worn out, they are unbolted and bores are drilled into new retread strips in alignment with the mounting bores in the drum. The new strips are then bolted to the drum.
These prior art tumblers suffer from several disadvantages. First, there are many bolts that must be dealt with individually both in removing the worn strips and when installing new strips. Second, it is necessary to drill bores in the new rubber strips to accommodate the bolts that secure them. Drilling rubber is difficult and time-consuming. Finally, in these prior art tumblers, the head of each bolt is fully exposed above the surface of the rubber. As a result, the tumbling blocks frequently strike bolt heads, which tends to knock off the galvanizing.